article: When you look up into the sky at night, have you ever felt that your eyes are playing tricks on   you? It seems that the stars are moving all the time.
  Actually, there is nothing wrong with your eyes. This twinkling effect is called scintillation  . Scintillation happens because of air movements in the earth's atmosphere  . Light is "bent  " when it travels through different parts of the earth's atmosphere. As the air in the earth's atmosphere is moving all the time, the light from the stars looks as if it is moving too.
  The same thing also happens to things on the ground. On a very hot and shiny day, if you look at the road, the image in the distance is not clear and things move slightly. You can also see the same effect if you drop a rock into water. The rock appears a little unclear under the moving water.
  This twinkling effect causes a lot of problems for astronomers   since they cannot _ the stars clearly. A telescope   was sent into space so that the air movements in the atmosphere could be avoided  . It took a long time to build the space telescope but finally in 1990, a huge space telescope called the Hubble Space Telescope was successfully sent into space. Since then, astronomers have many important observations that have helped people understand space better.
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question: What can you see when you drop a rock into the water?
options: The rock gets broken. The rock becomes unclear. The water becomes much polluted. The water does not move anymore.